Process of simultaneously cleaning and coating a photoconductive surface with a fluorinated hydrocarbon polymer

ABSTRACT

THE LIFE OF PHOTOCONDUCTIVE INSULATING LAYERS USED IN ELECTROPHOTOGRAPHIC COPYING PROCESS IN EXTENDED AND THEIR QUALITY IS MAINTAINED THROUGHOUT THEIR LIFE BY CONTACTING THE SURFACE AT LEAST PERIODICALLT DURING USE WITH A MATERIAL COMPRISING A FULORINATED HYDROCARBON POLYMER. FOR EXAMPLE, A TUFTED FIBROUS WEB OF POLYTETRAFLUOROETHYLENE IS HELD IN CONTACT WITH THE PHOTOCONDUCTIVE SURFACE SUCH THAT RELATIVE MOTION OCCURS BETWEEN THE FIBROUS WEB AND THE SUFACE.

g- 3, 1972 R. L. DUELTGEN ETAL 3,682,689

PROCESS OF SIMULTANEOUSLY CLEANING AND COATING A PHOTOCONDUCTIVE SURFACE WITH A FLUORINATED HYDROCARBON POLYMER Original Filed Sept. 26 1968 4? FIG. a

FIG. 1

FIG. 2

INVENTORS.

RAY L. DUELTGEN CARL A OUEENER United States Patent Ofice" 3,682,689 Patented Aug. 8, 1972 1 BEST AVAILABLE 3,682,689 PROCESS OF SIMULTANEOUSLY CLEANING AND COATING A PHOTOCONDUCTIVE SURFACE WITH A FLUORINATED HYDROCARBON POLYMER Ray L. Dueltgen, 713 Cumberland Road, and Carl A. glalsegger, 700 Cromwell Way, both of Lexington, Ky. Continuation of abandoned application Ser. No. 762,952, Sept. 26, 1968. This application July 2, 1971, Ser. No. 159,530 Int. Cl. B05c 1/06 US. Cl. 117-111 R v 7 Claims ABSTRACT OF THE DISCLOSURE The life of photoconductive insulating layers used in electrophotographic copying processes is extended and their quality is maintained throughout their life by contacting the surface at least periodically during use with a material comprising a fluorinated hydrocarbon polymer. For example, a tufted fibrous web of polytetrafiuoroethylene is held in contact with the photoconductive surface such that relative motion occurs between the'fibrous web and the surface.

BACKGROUND OF THE INVENTION This application is a continuation of application Ser.

No. 762,952, filed Sept. 26, 1968 and now abandoned.

Electrophotography using photoconductive insulating layers upon which an electrostatic image is formed, for example, as is described in US. Patent 2,297,691, has become embodied in a number of high speed copying processes. The photoconductive insulating layer is backed by a conductive layer and can be formed in the shape of a cylinder which is then rotated to bring the photoconductive surface to a number of stations involved in the electrophotographic process. An electrical potential is first applied across the photoconductive insulating layer. The charged photoconductive layer is then exposed imagewise to light and the electrical potential decays in the surface areas which are struck by light. The dark areas of the projected image retain their electrostatic charge and the image is then developed by exposing the surface of the photoconductive layer to small colored particles known as toner particles which have a charge opposite to that of the image. The charged toner particles are attracted to the charged image areas of the photoconductor surface and thereby develop the electrostatic image. The image can then be transferred from the photoconductor surface to a copy sheet. 7

A number of ways are employed to develop the electrostatic image as is well known in the art, such as cascade development described, for example, in US. Pat! 2,6l8,-

a copy sheet. Because it has not been found possible to inake a 100% transfer of toner to" the copy sheet, a portion of the image remains on the photoconductive surface and small amounts 'of finely divided toner particles also cling to the non imaged'areas. If not re'moved, this resid- COPY 2 ual image and background toner will appear on the following copy. Therefore, it is necessary to provide a means of maintaining the surface of the photoconductor free from residual toner particles or other foreign matter from one copying cycle to the next.

In the past, residual toner particles have been removed by cleaning, such as by physically contacting the surface of the photoconductor with either a renewable web or belt of a fibrous material, or with the bristles of a rotating cylindrical brush. The fiber materials employed have included, for example, animal fur, vegetable fibers, and synthetic fibers such as nylon, Dynel or cellulose derivatives. It has been found that while this cleaning removes the majority of the toner particles from the photoconductor on each cycle, it has been found to cause certain problems, the most notable of which is a tendency of the cleaning means employed to apparently contribute to the formation of a film of toner material on the surface of the photoconductor. This toner film eventually builds up over a period of from several hundred to several thousand copy cycles to a point where it seriously impairs the copy quality produced by the photoconductor because it results in the appearance of a dark background of toner on the copy sheet. It then becomes necessary to clean or replace the photoconductive surface which is inconvenient and costly in time and material. The cause of the contribution by the cleaning means to filming is not completely understood, but it is believed to result, at least in part, from frictional heating caused by the moving contact between the cleaning web or brush and the photo- 'conductor surface which acts to fuse some of the toner BRIEF SUMMARY OF THE INVENTION We have now discovered a method of maintaining the surface of a photoconductor substantially free from deleterious effects caused by toner filming thereon and a means which not only can act to clean residual toner particlesfrom the photoconductive surface, but instead of contributing to toner filming actually has a long term beneficial preventive effect in this respect.

'In accordance with this invention, a method is provided which extends the life and maintains the quality of a photoconductive layer comprising at least periodically contacting the surface of said photoconductive layer with a fluorinated hydrocarbon polymer to maintain a thin deposit of fluorinated hydrocarbon thereon.

Also provided are means for at least periodically contacting the surface with a fluorinated hydrocarbon polymer. A fibrous web or brush woven from filaments of a fluorinated hydrocarbon polymer has been found to be a particularly advantageous means for accomplishing the results achieved by the invention.

DESCRIPTION OF THE DRAWINGS layer by a coating of latex rubber. The resulting 3 DETAILED DESCRIPTION layer at least periodically with a fluorinated hydrocarbon 5 polymer. While the cause of the beneficial effect is not entirely understood, it has been observed that such contact causes a small amount of fluorinated hydrocarbon polymer to be deposited on the photoconductive surface. This deposit, which need be only a few molecules in thickness and therefore not detectable by ordinary means, has

been found to either prevent or greatly retard any build up of toner film on the surface of the photoconductive layer. After a time, a whitish haze may appear on the surface of the photoconductive layer. This haze does not interfere with the charging properties of the layer. The

haze is a very thin (about one micron or less thick) loosely adhered deposit of the fluorinated hydrocarbon polymer material which is soft and, therefore, easily abraided when placed in contact with the surface of the photoconductive layer. Care should be taken to avoid the build up of a relatively thick, clear, firmly adherent film of the fluorinated hydrocarbon polymer which may interfew with the charging properties of the photoconductive layer.

While any convenient means can be employed to contact the surface of the photoconductive layer with the fluorinated hydrocarbon polymer, because of the fact that the fluorine containing polymers are available in the form of filaments which can be woven by conventional carpet weaving machines into soft, tufted fibrous webs, it has been found advantageous to employ the fluorinated hydrocarbon polymers in the form of a web or brush. In this manner the benefiical effects of the treatment of the photoconductive layer with fluorinated hydrocarbon during use can be carried out simultaneously with the cleaning function which removes residual toner from the surface of the photoconductive layer. This eliminates the The fluorocarbon polymer webs or brushes in fact have been found to possess excellent cleaning properties when employed in accordance with the invention. If desired, a web can be employed which is a combination of fibers of a conventional'cleaning 'materialof naturalfur or synthetic fiber and fibers of the fluorocarbon polymer.

Suitable treating materials for the practice of'the-invention are fluorocarbon resins, such as, for example,

polytetrafluoroethylene, polyvinylfluoride, polyvinylidenemers of the type useful in the practice of the invention are sold under the tradename Teflon, and are-available in the form of filaments. Advantageously, the filaments are need to employ a separate conventional cleaning means.

fluoride, polychlorotrifluoroethylene, and copolymers of 'tetrafluoroethylene with tetrafluoropropylene, etc. Polycombined into multifilament strands and formed into a fibers are conventionaly cemented in place at the backing a soft, furlike material. 5

The density of the woven web is not particularly critical and will vary, depending upon the type of weave employed. For example, when employing a Wilton weave of 256 pitch, densities of from about 9,60071,440/2.5 (total denier'per strand/filaments per strand/twists per inch) and 16 picks per inch to about 1,200/ 180/ 2.5 (total denier per strand/filaments per strand/twists per inch) and 20 picks per inch have been used. A preferred density has been found to be about 3,600/540/2.5 (total denier per strand/filaments per strand/twists per inch). with 18 picks per inch. The fiber length is not critical and preferred fiber lengths (pile height) vary fromv about 1 /2 to inch.

In the embodiment shown in FIG. 1, where some of the dimensions are exaggerated for the purpose of illusweb is a '4 tration, a fibrous web 11 of polytetrafluoroethylene of medium density (256 pitch Wilton weave 3,600/540/2.5 and 18 picks per inch and a fiber length of /8 inch) com prising a series of tufts 13 and a cotton backing layer 7 :in FIG. 2 so that when the direction of relative movement between the web and the photoconductor surface is in the direction shown by the arrow, all portions of the photoconductor surface will-be equally contacted by the denser fiber area around the roots 12 of tufts 13, and channeling, which has been found to occur in the less denser fiber areas between the rows of tufts if they are oriented parallel to the direction of relative movement, is thereby avoided.

Turning now to FIG. "3, a typical clectrophotographic copying device is schematically shown in conjunction with an embodiment ofythe' invention. A cylindrical drum 21 is mounted for rotation on a shaft 22 and having on its outer periphery, 23 a photoconductive. insulating layer 25 which contains an organic or inorganic photoconductive material. The drum 21 is rotated to bring the photoconductive layer to the various stations associated with which issued on Dec. 16, 1969 as US. Pat. 3,484,237, and

assigned to the assignee of the invention. p A pre-exposure corona.unit 35 deposits a charge on the photoconductive material while it is maintained llJ.

'the dark. A document 27 is held in place on a transparent plate 29 and an image of the document is projected on the, surface of the photoconductive insulating layer 25 by means of ;an illuminated scanning station 811 and optics .33. The photoconductor is discharged at 37 in the portions struck by light to form the charged image correspondingto the document 27 and the image is developed at developer station 38 which serves to bring finely divided charged toner particles'into contact with the charged image on the surface of photoconductive layer 25. The developer station can, be any convenient developer means, such as, for example, a cascade jdeveloper unit, powder cloud developer unit, or a magnetic brush developer unit as is well known inthe art. The station illustrated at 38 is a cascade developer unit where a two component developer. composition is caused, to move across the surface of the photoconductive layer. The developer composition comprises relatively large carrier .particles and relatively small heat fixable marking particles of toner. The toner particles areattracted to, and

cling to the charged areas of the photoconductor layer.

At station 39 the toner image on the surface. of photoconductive layer 25 is transferred to-a plain paper sheet or web 41 with the assistance of atoner transfer corona unit 43. The paper is then separated ffromthe photoconductive layer and passed to a heating unit 45 which, acts to fix the toner image onto the paper. The residual toner particles are loosened by the discharge ,of a precle'an corona unit 47.1116 rotating photoconductive surface is then contacted by a driven counter-rotating cylindrical cleaning and treatmentbrush 49, whose lengthcorrespends-approximately to the width of the photoconductive layer on the drum, of the structure illustrated in .FIGS. 1 and 2. The brush is mounted for rotation in a the removed toner from the brush to a filter bag 52. Knock-off bar 53 aids in removing toner particles from the brush so that the brush remains relatively free from toner particles upon extended use. The engagement of the brush on the drum surface is readily determined by adjustment to give the best cleaning efiiciency depending upon the length and density of the particular web employed and the velocity of the brush over the photoconductive surface. In this respect, care must be exercised I Example 1 Using the apparatus shown in FIG. 3, and a 9600/ 1440/25 brush using the cascade development and employing a developer composition which was a mixture of resin coated sand as carrier particles and toner particles which were pigmented, polystyrene-n-butyl methacrylate copolymer particles (commercially available from Philip Hunt Chemical Company under the trademark Graph-O- -Print toner) and a brush speed of 1,250 r.p.m. and drum engagement of inch, no toner film was observed to occur on the surface of the photoconductive layer after 12,000 copies, although a white haze layer of fluorinated hydrocarbon polymer appeared after about 200 cycles which layer had no deleterious elfect on copy quality at the 12,000 cycle level.

In a control test the apparatus was used to make copies using identical conditions, except that the brush of the invention was replaced by a synthetic fiber brush of a copolymer of vinyl chloride and acrylonitrile available under the tradename Dynel. A marked filming of the photoconductor surface by the toner was observed after 2,000 copies and the loss of copy quality due to toner filming was so severe after 3,000 copies that the photoconductor surface required replacement.

Example 2 In order to demonstrate the use of the invention with an apparatus employing another development method, the cascade development unit of the apparatus of FIG. 3 was replaced with a magnetic brush unit employing a rotating magnetic metal cylinder as a core and a developer mix comprised of 230 micron mean diameter resin coated steel shot as carrier and [Hunt Graph-O-Print toner. The cleaning station was modified by replacing the single brush with a pair of driven counterrotating brushes having a pile of polytetrafluoroethylene /3" in length and a 256 pitch Wilton weave with a density of 3,600/540/2.5 held on a 1% inch diameter cardboard core. The brushes were mounted side by side in parallel with a As" engagement with the surface of the photoconductive layer and rotated at 1200 rpm. to sweep the removed toner back through the area between the brushes. The remainder of the copy apparatus was not changed. The copying apparatus was used to produce 22,000 copies with no toner film occurring on the photoconductive layer and no deterioration of copy quality.

In a control run the brushes were replaced by cleaning brushes of Dynel. After 1500 copies the surface of the photoconductive layer was so badly filmed with toner that the photoconductor surface required replacement.

In the foregoing embodiments of the invention the treatment of the photoconductor was carried out in combination with the normal toner cleaning function. The fluorinated hydrocarbon polymer filaments provide a continuous supply of treating material. The novel treatment method can also be accomplished by employing, for example, a separate treating web, fluorinated hydrocarbon polymer coated fibers, or other similar means to transfer and maintain a thin deposit of fluorinated hydrocarbon polymer on the surface of the photoconductive layer during use andsuch means are considered to be within the scope of the invention.

The invention has other advantages which extend the number of materials which can be used to develop electrostatic images. For example, various toner materials which have suitable properties from all standpoints, except that they cause excessive filming of the photoconductor and, therefore, were heretofore unsatisfactory for use in high speed automatic copying machines can now be employed by treating the photoconductor surface in the manner described in the invention.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A process for extending the life of a photoconductive surface through the simultaneous treatment of the photoconductive surface in conjunction with the cleaning thereof comprising cleaning said surface by contacting said surface with a fibrous member of a fluorinated hydrocarbon polymer at the time relative motion exists between said member and surface, wherein a portion of said polymer is transferred to said surface when relative motion exists between said member and said surface.

2. A process for extending the life of a photoconductive surface through the simultaneous treatment of the photoconductive surface in conjunction with the cleaning thereof comprising contacting said surface with a fibrous rotating fluorinated hydrocarbon polymer member whereby said member cleans said surface at the same time as a portion of said polymer is transferred to said surface.

3. A process for cleaning and extending the life of a photoconductive surface upon which toner is deposited for developing a latent image contained thereon comprising contacting said surface with a rotating brush of polytetrafluoroethylene whereby a film is deposited on said surface to minimize the effect of toner filming caused by said deposited toner and cleaning said surface at the same time said brush is contacting said surface.

4. A process for cleaning and extending the life of a photoconductive surface comprising:

providing a fibrous brush comprising a fluorinated hydrocarbon polymer in frictional contact with said surface and imparting relative motion between said surface and said brush whereby a film of fluorinated hydrocarbon polymer is deposited on said surface at the time said brush is cleaning said surface.

5. A process for depositing an overcoating of a fluorinated hydrocarbon polymer upon a photoconductive member of an electrophotographic apparatus comprising the steps of:

simultaneously cleaning said photoconductive member and depositing said polymer on said photoconductive member by contacting a cleaning means comprised of said fluorinated hydrocarbon polymer with said photoconductive member and creating relative motion therebetween as an incident of the operation of said electrophotographic apparatus, thereby abrading a portion of said polymer from said cleaning means and transferring said portion to said photoconductive member while simultaneously removing undesired foreign materials from the surface of said photoconductive member.

6. A process of maintaining an overcoating of a fluorinated hydrocarbon polymer upon a photoconductive member and comprising the steps of simultaneously cleaning said photoconductive member and depositing said polymer on said photoconductive member by contacting a cleaning means comprised of said fluorinated hydrocarbon polymer with said photoconductive member and creating relative motion therebetween, frictionally removing a portion of said polymer from said cleaning means and transferring said portionv to said photoconductive member while simultaneously removing undesired foreign materials' from the surface of said photoconductive member, whereby said overcoating is supplemented by the additive eifect of said depositing, thereby overcoming the removal of said overcoat material from said photoconductive member.

7. A process for extending the life of a photoconductive surface through the simultaneous treatment of the photoconductive surface in conjunction with the cleaning thereof comprising:

cleaning said surface by contacting said surface with a member of a fluorinated hydrocarbon polymer at the time relative motion exists between said memher and said surface wherein a portion of said polymer is transferred to said surface when relative motion exists between said member and said surface. 20

7 References Cited UNITED STATES PATENTS 2,860,048 11/1958 Deubner 96-1.5 3,146,145 8/1964 Kinsella 96-1.5 X 3,251,686 5/1966 Gundlach 117-218 X 2,284,590 5/1942 Rogers 118--V76 X 3,130,933 4/1964 Pillsbury et.al. 118-77 X 3,318,212 5/1967 Rubin 118-76X FOREIGN PATENTS 1,002,126 8/1965 Great Britain 118-77 GEORGE F. LESMES, Primar Examiner R. E. MARTIN, Assistant Examiner U.S. C1. X.R. I

96-1 R, 1.4; 1l7-DIG 1, 111 C; 118-76; 134-6 PO-IOW I I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,682 .Dated August 8 1972 Inventor-(s) Ray L. Dueltgen and Carl A. Queener It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 8 after "'40503" insert assignors to International Business Machines Corporation, Armonk, N.Y. a corporation of New York.-.

Signed and sealed this 17th day of April 1975.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

